PROJECT SUMMARY: Neurodevelopmental disorders including Schizophrenia and Autism spectrum disorders (ASD) are chronic and debilitating, with relatively unknown etiology and pathophysiology. Recent progress towards understanding the genetic architecture of these disorders at the population level has led to the identification of many genetic risk factors. However, in most cases the molecular mechanism of risk and the relevant functions of the identified genes are not known and therefore identifying therapeutic targets remains difficult. In our proposal we have outlined a roadmap for the identification of therapeutic targets for psychiatric disorders and provide preliminary data that suggests our approach has merit. We propose to use two model systems, a cell autonomous model in which expression of the schizophrenia and ASD gene TCF4 (transcription factor 4) is manipulated using in utero electroporation and a mouse model that has a constitutive germline truncation of one TCF4 allele that models Pitt-Hopkins syndrome (PTHS). We will characterize the resulting neuronal phenotypes using brain slice electrophysiology, cell biology, and confocal imaging. Identified phenotypes will be evaluated as potentially pathophysiological and the development of therapeutic treatments will be based on our emerging understanding of the molecular mechanism responsible. In Aim1, we hypothesize that TCF4 transcriptionally regulates intrinsic neuronal excitability and therefore suppression of TCF4 expression will result in abnormal neuronal physiology relevant to PTHS. Our preliminary data suggest that in utero knockdown of TCF4 in layer 2/3 pyramidal cells of the PFC results in abnormal intrinsic excitability and ectopic spike-frequency adaptation. We show the cellular mechanisms of these phenotypes are associated with an increase in the afterhyperpolarization (AHP). Using a novel molecular profiling technique (iTRAP) we have identified two candidate ion channels that are regulated by TCF4 and may underlie cognitive phenotypes observed in PTHS. To validate these target genes, we propose pharmacological rescue and molecular phenocopy experiments. In Aim 2, we propose to use a mouse model of PTHS. Our preliminary data indicates PFC layer 2/3 neurons from TCF4+/tr mice show similar intrinsic excitability deficits to what we observe when TCF4 is knockdown using shRNA/Crispr constructs. We propose cellular and molecular experiments to identify the mechanisms underlying this phenotype with the future goal of using pharmacology to rescue behavioral deficits in these mice. In Aim 3, we propose to identify how the neural transcriptome is altered across development in PTHS mouse model. We hypothesize that identifying molecular consequences of TCF4+/tr on the neural transcriptome will provide mechanistic and pathological insight about PTHS and potentially other idiopathic ASDs. Together, these Aims are designed to identify therapeutic targets for treatment of PTHS.